Combustion chemical vapor deposition (combustion CVD) is a relatively new technique for the growth of coatings. Combustion CVD is described, for example, in U.S. Pat. Nos. 5,652,021; 5,858,465; and 6,013,318, each of which is hereby incorporated herein by reference in its entirety.
Conventionally, in combustion CVD, precursors are dissolved in a flammable solvent and the solution is delivered to the burner where it is ignited to give a flame. Such precursors may be vapor or liquid and fed to a self-sustaining flame or used as the fuel source. A substrate is then passed under the flame to deposit a coating.
There are several advantages of combustion CVD over traditional pyrolytic deposition techniques (such as CVD, spray and sol-gel, etc.). One advantage is that the energy required for the deposition is provided by the flame. Another advantage is that combustion CVD techniques do not necessarily require volatile precursors. If a solution of the precursor can be atomized/nebulized sufficiently (e.g., to produce droplets and/or particles of sufficiently small size), the atomized solution will behave essentially as a gas and can be transferred to the flame without requiring an appreciable vapor pressure from the precursor of interest.
It will be appreciated that combustion deposition techniques may be used to deposit metal oxide coatings (e.g., single-layer anti-reflective coatings) on glass substrates, for example, to alter the optical and other properties of the glass substrates (e.g., to increase visible transmission). To this end, conventional combustion deposition techniques were used by the inventors of the instant application to deposit a single layer anti-reflective (SLAR) film of silicon oxide (e.g., SiO2 or other suitable stoichiometry). The attempt sought to achieve an increase in light transmission in the visible spectrum (e.g., wavelengths of from about 400-700 nm) over clear float glass with an application of the film on one or both sides of a glass substrate. In addition, increases in light transmission for wavelengths greater the 700 nm are also achievable and also may be desirable for certain product applications, such as, for example, photovoltaic solar cells. The clear float glass used in connection with the description herein is a low-iron glass known as “Extra Clear,” which has a visible transmission typically in the range of 90.3% to about 91.0%. Of course, the examples described herein are not limited to this particular type of glass, or any glass with this particular visible transmission.
The combustion deposition development work was performed using a conventional linear burner. As is conventional, the linear burner was fueled by a premixed combustion gas comprising propane and air. It is, of course, possible to use other combustion gases such as, for example, natural gas, butane, etc. The standard operating window for the linear burner involves air flow rates of between about 150 and 300 standard liters per minute (SLM), using air-to-propane ratios of about 15 to 25. Successful coatings require controlling the burner-to-lite distance to between about 5-50 mm when a linear burner is used.
Typical process conditions for successful films used a burner air flow of about 225 SLM, an air-to-propane ratio of about 19, a burner-to-lite distance of 35 mm, and a glass substrate velocity of about 50 mm/sec.
FIG. 1 is a simplified view of an apparatus 100 including a linear burner used to carry out combustion deposition. A combustion gas 102 (e.g., a propane air combustion gas) is fed into the apparatus 100, as is a suitable precursor 104 (e.g., via insertion mechanism 106, examples of which are discussed in greater detail below). Precursor nebulization (108) and at least partial precursor evaporation (110) occur within the apparatus 100 and also may occur external to the apparatus 100, as well. The precursor could also have been delivered as a vapor reducing or even eliminating the need for nebulization The flame 18 may be thought of as including multiple areas. Such areas correspond to chemical reaction area 112 (e.g., where reduction, oxidation, and/or the like may occur), nucleation area 114, coagulation area 116, and agglomeration area 118. Of course, it will be appreciated that such example areas are not discrete and that one or more of the above processes may begin, continue, and/or end throughout one or more of the other areas.
Particulate matter begins forming within the flame 18 and moves downward towards the surface 26 of the substrate 22 to be coated, resulting in film growth 120. As will be appreciated from FIG. 1, the combusted material comprises non-vaporized material (e.g., particulate matter), which is also at least partially in particulate form when coming into contact with the substrate 22. To deposit the coating, the substrate 22 may be moved (e.g., in the direction of the velocity vector). Of course, it will be appreciated that the present invention is not limited to any particular velocity vector, and that other example embodiments may involve the use of multiple apparatuses 100 for coating different portions of the substrate 22, may involve moving a single apparatus 100 while keeping the substrate in a fixed position, etc. The burner 110 is about 5-50 mm from the surface 26 of the substrate 22 to be coated.
Using the above techniques, the inventor of the instant application was able to produce coatings that provided a transmission gain of 1.96% or 1.96 percentage points over the visible spectrum when coated on a single side of clear float glass. The transmission gain may be attributable in part to some combination of surface roughness increases and air incorporation in the film that yields a lower effective index of refraction.
Although a percent change in Tvis gain of about 2% is advantageous, further improvements are still possible. For example, optical modeling of these layers suggests that an index of refraction of about 1.33 for coatings that are about 100 nm thick should yield a transmission gain of about 3.0-3.5% or about 3.0-3.5 percentage points. The index of refraction of bulk density (e.g., no or substantially no air incorporation) silicon dioxide is nominally between about 1.45-1.5.
Furthermore, it would be desirable to approximate the properties obtained via sol-gel techniques. Sol-gel derived coatings of metal oxides (e.g., of silicon oxide) have been found to provide an increase in transmission of nominally about 3.5% over the visible spectrum when coated on a single side of clear float glass. For example, sol-gel coatings having a silicon oxide (e.g., SiO2 or other suitable stoichiometry) based matrix which had silica nano-particles embedded therein were produced. The interaction of the silicon oxide matrix with the nano-particles produced a microstructure that gave rise to the coating's excellent AR properties.
Thus, it will be appreciated that there is a need in the art for improved techniques for depositing metal oxide coatings (e.g., anti-reflective coatings of, for example, silicon oxide) on glass substrates via combustion deposition, for combustion deposition techniques that yield coatings exhibiting properties comparable to those produced by the sol-gel processes noted above, and/or for metal oxide coatings having improved microstructures (e.g., metal oxide coatings having nano-particles embedded therein). It also may be possible to use the techniques described herein as a different method for controlling microstructures, in general.
According to certain example embodiments, to improve the percent change in Tvis gain beyond the current levels of 1.96%, metal oxide coatings (e.g., silicon oxide coatings) may be produced using techniques that cause the microstructure of the coatings to emulate the microstructures of sol gel deposited coatings. The coatings produced in accordance with certain example embodiments possess an enhanced transmission increase over previously combustion deposition produced single-layer anti-reflective (SLAR or single-layer AR) coatings. This may be accomplished in certain example embodiments by providing intermixed or graded metal oxide coatings through nano-particle matrix loading of metal oxide coatings via combustion deposition. More particularly, it may be accomplished in certain example embodiments by using a precursor and by depositing surface passivated nano-particles from a finely atomized solution or colloid (which may be of or include the same or different metals) that respectively produce small nucleation particle size distributions and nano-particle size distributions to grow a coating where there is an increased number of air gaps with increased particle size, thereby reducing the index of refraction of the coating.
In certain example embodiments of this invention, a method of forming a coating on a glass substrate using combustion deposition is provided. A glass substrate having at least one surface to be coated is provided. A metal oxide based precursor and a metal oxide based nano-particle inclusive solution or colloid to be combusted by a flame are introduced. At least a portion of the precursor and the nano-particle inclusive solution or colloid are combusted to respectively form first and second combusted materials. The first and second combusted materials each comprise non-vaporized material. The glass substrate is provided in an area so that the glass substrate is heated sufficiently to allow the first and second combusted materials to form growths directly or indirectly, on the glass substrate. The first and second combusted materials respectively produce nucleation particle size distributions and nano-particle size distributions in forming the coating. The coating comprises a metal oxide matrix including metal oxide nano-particles embedded therein.
In certain example embodiments, a method of making a coating on a substrate using combustion deposition is provided. A glass substrate having at least one surface to be coated is provided. A metal oxide based precursor and a metal oxide based nano-particle inclusive solution or colloid to be combusted by a flame are introduced. At least a portion of the precursor and the nano-particle inclusive solution or colloid are combusted to respectively form first and second combusted materials. The first and second combusted material each comprise non-vaporized material. The glass substrate is provided in an area so that the glass substrate is heated sufficiently to allow the first and second combusted materials to form growths directly or indirectly, on the glass substrate. The precursor and the nano-particle inclusive solution or colloid respectively produce nucleation particle size distributions and nano-particle size distributions in forming the coating. The precursor and/or the nano-particle inclusive solution or colloid includes silicon oxide.
In certain example embodiments, a coated article including a coating supported by a glass substrate is provided. A combustion deposition deposited growth is arranged such that the growth comprises a matrix of small dense nucleation particle size distributions embedded with nano-particle size distributions. The nano-particle size distributions are deposited from a nano-particle inclusive solution or colloid. The coating increases visible transmission of the glass substrate by at least about 2.0% when coated on one side thereof.
In certain example embodiments, a method of making a coated article including a coating supported by a glass substrate is provided. A film comprising a metal oxide matrix having nano-particles embedded therein is formed. The metal oxide matrix is formed directly or indirectly on the substrate by combustion deposition depositing, via a precursor, a first combusted material that would produce small nucleation particle size distributions if coated independently while also combustion deposition depositing, via a nano-particle inclusive solution or colloid, in or on the small nucleation particle size distributions, a nano-particle size distribution. The second combusted material may or may not produce large agglomerate nano-particle size distributions if coated independently.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.